1. Field of the Invention
The present invention relates generally to firearms, and more particularly toward a manually reciprocated bump-stock accessory for semi-automatic firearms.
2. Related Art
Various techniques and devices have been developed to increase the firing rate of semi-automatic firearms. Many of these techniques and devices make use of the concept known as “bump firing”, which is the manipulation of the recoil of the firearm to rapidly activate the trigger. One such bump firing technique is known as the “belt loop” method. To execute the belt loop method, the operator first places the firearm next to his or her hip and hooks one finger through both the trigger mechanism and a belt loop in the his or her clothing. The opposite hand is placed on the hand guard, which is attached to the barrel of the firearm. When the firearm is pushed forward by the operator, the trigger is activated by the finger to discharge a bullet. The recoil from the bullet pushes the firearm backwards away from the trigger finger, allowing the trigger to re-set. Forward force must be applied to the hand guard in order to activate the firing mechanism for each round that is fired. However, this may be achieved in very rapid succession.
Although able to achieve a high rate of firing, the belt loop has many safety and accuracy issues. For example, to correctly operate many firearms with the belt loop method, the operator's arm must be placed in the path of hot gasses being expelled from the ejection port of the firearm. This could lead to skin burns or possibly pinch the operator's sleeve or skin in the action. Another issue with the belt loop method arises because the operator cannot have a firm grip on the stock or the pistol grip of the firearm. Because the belt loop method only works if the firearm is held loosely with one hand, and the chances of the operator losing control of the firearm are greatly amplified. Because of this unnatural and unbalanced firing grip, the firearm is very difficult to aim and control during the belt loop method.
Commercial devices are also available for assisting in the bump firing concept, including the HELLSTORM 2000 and TAC Trigger. Both of these are small devices that mount to the trigger guard of the firearm and use springs to aid in quickly resetting the trigger while the firearm is bump fired, as described above. However, the same safety and accuracy issues of the belt loop method apply to these devices because the firearm cannot be held securely with the trigger hand or the stock of the firearm.
Another device for increasing the firing rate of a semi-automatic firearm is shown in U.S. Pat. No. 6,101,918, issued to Akins on Aug. 15, 2000 (“Akins '918”). Akins '918 shows a handle for rapidly firing a semi-automatic firearm having a trigger. The handle of Akins '918 extends from the stock all the way to the barrel of the firearm and a spring rod guide system supports the receiver and barrel of the firearm for longitudinal movement of the firearm relative to the handle. The handle includes a grip portion for holding the firearm. Springs are disposed between the handle and the firearm for continuously biasing the firearm in a forward direction. The handle further includes a finger rest against which the shooter's trigger finger stops after the trigger is initially pulled. In operation, the operator places their trigger finger (typically an index finger) against a trigger and gently squeezes or pulls the trigger rearwardly to discharge a first bullet. The recoil of the firearm forces the receiver and trigger mechanism longitudinally backward relative to the handle at the same time the shooter's trigger finger lands in a stationary position against the rest. The springs are carefully sized to the ammunition so as to be easily overcome by the recoil energy of a fired bullet. Continued rearward movement of the receiver and trigger assembly under the influence of recoil creates a physical separation between the shooter's finger (now immobilized by the rest) and the trigger, thus allowing the trigger mechanism of the firearm to automatically reset. As the recoil energy subsides, the constant biasing force of the springs eventually becomes sufficient to return the receiver and trigger portions of the firearm back to the starting position without any assistance from the operator. In the meantime, if the operator's trigger finger remains immobilized while the springs push the firearm back to its starting position, the reset trigger will collide with the finger and automatically cause the firearm to discharge another round, thus repeating the firing cycle described above. So long as the shooter's finger remains in place against the rest and there is an ample supply of ammunition, the firearm will continue firing rapid successive rounds without any additional human interaction or effort. One significant drawback of the Akins '918 construction is that automatic mechanisms of this type have been scrutinized for violating federal firearms laws. Another drawback is that different spring sizes (i.e., different resistance characteristics) may be required from one unit to the next depending on the type of ammunition used so that the springs do not overpower the recoil energy. This of course introduces inventory complexities.
A still further example of non-conventional shooting methods may be found by reference to U.S. Pat. No. 7,225,574 to Crandall et al., issued Jun. 5, 2007. In this case, which is not intended for semi-automatic type firearms, a shooter's muscle power is used to shuttle portions of a firing unit back and forth much like a traditional pump-action shotgun. A trigger mechanism is configured to be stimulated on the rearward pull-stroke, causing the ammunition to discharge. The forward push-stroke results in ejection of the spent shell casing. One particular disadvantage of this arrangement is that the natural recoil force generated by the discharge event is compounded by the shooter's pull-stroke. This may have a disadvantageous effect on aiming accuracy, particularly in rapid, multi-round volley shooting scenarios. It will therefore be appreciated that the shooting method of Crandall et al. is not conducive to rapid fire shooting as is common with semi-automatic firearms.
There exists a continuing need for further improvements in devices allow the operator to practice new and interesting ways to shoot firearms in a legal and safe manner, to increase the firing rate of semi-automatic firearms without compromising the safety of the operator or the accuracy of the firearm, which are generally universally functional without respect to ammunition type, and which are sufficiently distinguished from a fully automatic weapon so as to fall within compliance of federal firearms regulations. There exists further a need for an improved interface device or system disposed operatively between the firing unit of a firearm and the rear stock or grip portion of a firearm that is durable, sturdy, and not prone to binding in use.